Nickel nanoparticles

ABSTRACT

Nickel nanoparticles including an aqueous solution including a nickel precursor, a surfactant, a hydrophobic solvent, and distilled water, the hydrophobic solvent being one or more compounds selected from the group consisting of hexane, cyclohexane, heptane, octane, isooctane, decane, tetradecane, hexadecane, toluene, xylene, 1-octadecene, and 1-hexadecene; a compound including hydrazine which is added to the aqueous solution to form a nickel-hydrazine complex; and a reducing agent added to the compound including the nickel-hydrazine complex.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional and claims priority to U.S. applicationSer. No. 11/708,508, filed Feb. 21, 2007, which in turn claims thebenefit of Korean Patent Applications No. 10-2006-0032632 filed on Apr.11, 2006 and No. 10-2006-0078618 filed on Aug. 21, 2006, with the KoreaIntellectual Property Office, the contents of which are incorporatedhere by reference in their entirety.

BACKGROUND

1. Field

The present invention relates to a nickel nanoparticles, and inparticular, to uniform nickel nanoparticles having superior dispersionstability.

2. Description of the Related Art

Recently, according to the miniaturization of electrical machines andapparatus, it is highly required for electrical parts to beminiaturized. Accordingly, in case of Multi-Layer Ceramic Condenser(MLCC), the miniaturized that have high capacity are required, also incase of circuit boards, multilayer boards with high density andhigh-integration are required.

As to these MLCC and circuit board, precious metals such as silver,platinum or palladium have been used for inside conducting material orthe electrode material. However, they are substituted with nickelparticles for reducing production cost. In MLCC among these, a nickelelectrode layer has lower density in comparison with the packing densityof the molding product in the powder metallurgy and has higher degree ofcontraction according to sintering in curing than conducting layer,which cause high defective rate due to short of the nickel electrodelayer or disconnection of wiring. To prevent these problems, the nickelpowder should be fine particles, have a uniform narrow range of particledistribution, and exhibit superior particle distribution withoutagglomeration. For this, a method of manufacturing nickel nanoparticleshaving superior dispersion stability and uniform size is needed.However, the existing methods for manufacturing nickel nanoparticlescould not provide nanoparticles having superior dispersion stability anduniformity of below 100 nm size.

According to an existing embodiment, though a method where particles arereduced by hydrogen under at a high temperature of about 1000° C. isprovided, this method is not enough to be applied to internal electrodeor internal wiring since its thermal history under a high temperatureforces simultaneous generation and growth of particle so that theparticles thus produced have a wide range of particle distribution andlarge particles of 1 micron among them. Further, according to anotherexisting embodiment, though manufacturing of the micropowder havingsub-micron level according to the wet reduction method is possible, thenanoparticles thus produced may be unequal due to plentiful variables ofthe reaction. Also the surface of the micropowder is not smooth, andthough they may be produced in 200 nm-1 μm size, it is difficult toproduce uniform particles of below 100 nm size.

SUMMARY

As a solution to the foregoing problems, an aspect of the inventionprovides a method of manufacturing nickel nanoparticles and nickelnanoparticles thus produced, having uniform size, superior dispersionstability and smooth surface, by reducing after forming anickel-hydrazine complex in a reverse microemulsion.

Further, another aspect of the invention provides a method ofmanufacturing nickel nanoparticles and nickel nanoparticles thusproduced, having a narrow dispersion stability of below 100 nm,preferably 10-50 nm.

Additional aspects and advantages of the present general inventiveconcept will be set forth in part in the description which follows and,in part, will be apparent from the description, or may be learned bypractice of the general inventive concept.

According to an embodiment of the invention, the invention may provide aproduction method of nickel nanoparticles including: forming an aqueoussolution including nickel precursor, surfactant, and hydrophobicsolvent; forming nickel-hydrazine complex by adding a reducing agentthat includes hydrazine to the mixture; and producing nickelnanoparticles by adding a reducing agent to the mixture that includesthe nickel-hydrazine complex.

Here the nickel precursor may be one or more compounds selected from thegroup consisting of NiCl₂, Ni(NO₃)₂, NiSO₄, and (CH₃COO)₂Ni. Here, thesurfactant may be one or more compounds selected from the groupconsisting of cetyltrimethylammonium bromide, sodium dodecyl sulfate,sodium carboxymethyl cellulose, and polyvinylpyrrolidone. The surfactantmay further include one or more cosurfactants selected from the groupconsisting of ethanol, propanol, and butanol. Here, the hydrophobicsolvent may be one or more compounds selected from the group consistingof hexane, cyclohexane, heptane, octane, isooctane, decane, tetradecane,hexadecane, toluene, xylene, 1-octadecene, and 1-hexadecene.

Here, the nickel precursor may be included by 0.1-10 parts by weightwith respect to 100 parts by weight of the aqueous solution.

Here, the surfactant may be included by 0.1-20 mole with respect to 1mole of the distilled water that is added to the aqueous solution.

Further, the cosurfactant may be included by 20-40 part by weight withrespect to 100 parts by weight of the distilled water.

Here, the hydrophobic solvent may be included by 30-60 parts by weightwith respect to 100 parts by weight of the aqueous solution.

Further, the compound including the hydrazine may be one or morecompounds selected from the group consisting of hydrazine, hydrazinehydrate, and hydrazine hydrochloride. According to an embodiment, thecompound including the hydrazine may be included by 1-10 moles withrespect to 1 mole of nickel ions supplied by the nickel precursor.

Here, the reducing agent may be sodium borohydride. According to anembodiment, the sodium borohydride may be included by 0.1-1 mole withrespect to 1 mole of nickel ion supplied by the nickel precursor.

Further, the step of forming the aqueous solution to the step ofproducing nickel nanoparticles may be performed at 25-60° C., and thestep of producing nickel nanoparticles may be performed for 0.5-2 hours.

Here, 10-50 nm of uniform particles having smooth surface and superiordispersion stability may be generated.

According to another aspect of the invention, in a manufacturing methodof nickel nanoparticles by reverse microemulsion method, the inventionmay provide a method of producing nickel nanoparticles having uniformsize, superior dispersion stability and smooth surface, the methodincludes: forming nickel hydrazine complex with a compound havinghydrazine; and reducing this nickel hydrazine complex.

According to another aspect of the invention, the invention may providenickel nanoparticles manufactured by the method set forth above.

Here, the invention may provide 10-50 nm of uniform nickelnanoparticles, having smooth surface and superior dispersion stabilityand including 90-97 weight % of nickel content.

According to another aspect of the invention, the invention may provideconductive ink including nickel nanoparticles set forth above.

According to another aspect of the invention, the invention may providemulti layer ceramic condenser including nickel nanoparticles set forthabove as an electrode material.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the present generalinventive concept will become apparent and more readily appreciated fromthe following description of the embodiments, taken in conjunction withthe accompanying drawings of which:

FIG. 1 is a graph representing the result of XRD analysis for the nickelnanoparticles produced according to an embodiment;

FIG. 2 is a graph representing the result of TGA analysis for the nickelnanoparticles produced according to an embodiment;

FIG. 3 is a graph representing the result of particle distribution ofthe metal nanoparticles produced according to embodiments;

FIG. 4 is a photo representing the results of SEM analysis for the metalnanoparticles produced according to example 1;

FIG. 5 is a photo representing the results of SEM analysis for the metalnanoparticles produced according to example 2; and

FIG. 6 is a photo representing the results of SEM analysis for the metalnanoparticles produced according to example 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present invention will be described inmore detail with reference to the accompanying drawings.

Hereinafter, the method of producing nickel nanoparticles and nickelnanoparticles thus produced according to the present invention will bedescribed specifically. Before explaining the embodiments of theinvention, descriptions about reverse microemulsion will be given first.

In case of a non-soluble compound is dissolved in water or a hydrophilicmaterial by adding a surfactant, micelles expand as the non-solublecompound becomes soluble. Here, the micelle system expanded by thesolubilization is called as microemulsion. This microemulsion is athermodynamically stable system, which has an oil-in-water form that themicelles are expanded in water or a hydrophilic system, a water-in-oilform that reverse micelles solubilizes a large amount of water or ahydrophilic material to expand in an oil or a hydrophobic system. Amethod using this water-in-oil form is called as a reverse microemulsionmethod.

The invention is about a method of forming nano sized uniform dropletsproduced by a surfactant which is introduced by this reversemicroemulsion method.

Nickel nanoparticles having smooth surface and superior dispersionstability can be manufactured since the nickel nanoparticles aremanufactured by first adding a compound including hydrazine in thesemicro droplets to form complexes, and then reducing these complexes togenerate uniform nickel particles while preventing agglomeration withother nanoparticles. For this, a cosurfactant may be added according toan embodiment of the invention.

The method according to the invention includes forming an aqueoussolution including a nickel precursor, a surfactant, and a hydrophobicsolvent, forming a nickel-hydrazine complex by adding a compound thatincludes hydrazine to the mixture, manufacturing nickel nanoparticles byadding an reducing agent to the mixture that includes thenickel-hydrazine complex.

The method of the invention is different from the existing method thatproduces nanoparticles by reverse microemulsion, since nickel complexesare first formed and then reduced in order to manufacture nano-sizeduniform particles stably. Further, through this procedure, there is anadvantage that nickel nanoparticles having superior dispersion stabilitycan be obtained.

Hereinafter, each step will be described in detail.

First, preparing reverse microemulsion with a nickel precursor thatincludes nickel ions and a surfactant is performed. Here, any compoundthat include nickel ions may be appropriately used for the nickelprecursor without limitation, preferably salts of nickel. Examples ofthe nickel salts may include NiCl₂, Ni(NO₃)₂, NiSO₄, (CH₃COO)₂Ni, andmixtures thereof. The nickel precursor is added by 0.1-10 parts byweight with respect to 100 parts by weight of the total aqueoussolution. If the nickel precursor is added by less than 0.1 part byweight, amount of generated nickel ions is so low that it may not beeffective, and if this is added by more than 10 parts by weight,generated particles agglomerate each other, which is not proper to formnanoparticles. Here, the lower content of the nickel precursor becomes,the smaller nickel nanoparticles may be formed.

As the surfactant, cetyltrimethylammonium bromide (CTAB), sodiumdodecylsulfate (SDS), sodium carboxymethyl cellulose (Na-CMC),polyvinylpyrrolidone (PVP) or mixtures thereof, may be used. Besidesthese surfactants, a cosurfactant can be added to form micro micellesstably. The cosurfactant may be an alcohol such as ethanol, propanol, orbutanol. Here, the surfactant may be added by 0.1-20 moles with respectto 1 mole of distilled water that added in the aqueous solution, andthis ratio is preferable since the surfactant can enclose sufficientlywater droplets. Here, the higher content of the surfactant becomes, thesmaller nickel nanoparticles can be formed. Further, the cosurfactantmay be added by 20-40 parts by weight with respect to 100 parts byweight of the distilled water. If it is added by less than 20 parts byweight, it cannot stabilize microemulsions, and if it is added by morethan 40 parts by weight, it may interrupt the function of surfactant andstable formation of microemulsion.

The nickel precursor and surfactant are mixed with hydrophobic solventand distilled water, wherein for the hydrophobic solvent,hydrocarbon-based compounds such as hexane, cyclohexane, heptane,octane, isooctane, decane, tetradecane, hexadecane, toluene, xylene,1-octadecene, or 1-hexadecene may be used individually or by mixing. Thehydrophobic solvent may be added by 30-60 parts by weight with respectto 100 parts by weight of the aqueous solution, since stablemicroemulsion including nickel ions may be formed if the hydrophobicsolvent is added within this range.

Next, forming nickel complexes in the reverse microemulsion isperformed. For this, a compound including hydrazine is added, forexample, hydrazine, hydrazine hydrate, hydrazine hydrochloride may beused individually or by mixing. Here, the hydrazine has the structure ofNH₂NH₂, the hydrazine hydrate NH₂NH₂.nH₂O, the hydrazine hydrochlorideNH₂NH₃Cl. The compound including hydrazine may be added by 1-10 moleswith respect to 1 mole of nickel ions supplied from the nickelprecursor. If it is added by less than 1 mole, the nickel complex is notsufficiently formed, and if it is added by more than 10 moles, it is notappropriate in aspect of efficiency.

Then, forming nickel particles by adding a reducing agent to the reversemicroemulsion is performed. The reducing agent may be sodium borohydride(NaBH₄). Here, sodium borohydride may be added by 0.1-1 mole withrespect to 1 mole of nickel ions. If it is added by less than 0.1 mole,nickel-hydrazine complexes are not reduced sufficiently, and if it isadded by more than 1 mole, it causes side excessive side. The reactionis performed for 0.5-2 hours after adding the reducing agent to formnanoparticles having narrow particle distribution of below 100 nm. If ittakes less than 0.5 hour, the nickel ions are not sufficiently reduced,and if it takes more than 2 hours, nickel particles inappropriatelyovergrow and become unequal. The reaction is performed at 25-60° C., athigher than 60° C., the reaction occurs so rapidly that it is difficultto not only obtain uniform nanoparticles but control the growth ofparticles.

The method may further include separating the nickel nanoparticlesmanufactured by these procedure from the reverse microemulsion, andwashing and drying the nanoparticles thus separated. The separating,washing, and drying may be performed by conventional methods that areused in the related art, e.g., centrifugation for separation, acetoneand distilled water for washing, and a vacuum drying oven for drying.

Nickel nanoparticles and the method for manufacturing them weredescribed above, more detailed descriptions will be given in greaterdetail with reference to specific examples.

Example 1

Nickel chloride 18 g, PVP 18 g, ethanol 150 g, and toluene 150 g wereadded to 300 g of distilled water and the aqueous mixture was stirred at40° C. to produce reverse microemulsion. 40 g of hydrazine hydrate wasadded to the reverse microemulsion aqueous solution and it was stirredfor 30 minutes to form nickel-hydrazine complex. 0.04 mole of NaBH₄ wasadded to the reverse microemulsion including the nickel-hydrazinecomplex, and it was stirred for 1 hour to produce nickel particles byreduction. Nickel nanoparticles were separated from the reversemicroemulsion by centrifugation. After washing the separatednanoparticles with acetone and distilled water 3 times, nickelnanoparticles were obtained by drying in a vacuum drying oven at 50° C.for 3 hours.

A graph representing the result of X-Ray diffraction examination (XRD)for nickel nanoparticles manufactured by example 1 is illustrated inFIG. 1. Referring to FIG. 1, it is shown that pure nickel crystals weregenerated without impurities and oxidized substances.

Further, a graph representing the result of thermogravimetric analysis(TGA) for the nickel nanoparticles produced by example 1 is illustratedin FIG. 2. Referring FIG. 2, it is shown that the content of organicsubstance is 3-10 weight % of the formed nickel nanoparticles. Namely,it is shown that nickel occupies 90-97 weight % of the formed nickelnanoparticles.

Further, the result of particle distribution of nickel nanoparticlesproduced by example 1 is illustrated in FIG. 3. Referring FIG. 3, it isshown that uniform nanoparticles with narrow particle distribution weregenerated.

Further, a photo of Scanning Electron Microscope (SEM) of nickelnanoparticles produced by example 1 is illustrated in FIG. 4. ReferringFIG. 4, it is shown that round uniform nanoparticles of 30-40 nm sizewere generated.

Example 2

Nickel chloride 18 g, CTAB 20 g, ethanol 150 g, and toluene 150 g wereadded to 300 g of distilled water, and the aqueous mixture was stirredat 40° C. 30 g of hydrazine hydrate was added to the reversemicroemulsion and it was stirred for 30 minutes to form nickel-hydrazinecomplex. 0.03 mole of NaBH₄ was added to the reverse microemulsionincluding the nickel-hydrazine complex, and it was stirred for 1 hour toproduce nickel particles by reduction. Nickel nanoparticles wereseparated from the reverse microemulsion by centrifugation. Afterwashing the separated nanoparticles with acetone and distilled water 3times, nickel nanoparticles were obtained by drying in a vacuum dryingoven at 50° C. for 3 hours.

Further, a photo of Scanning Electron Microscope (SEM) of nickelnanoparticles produced by example 2 is illustrated in FIG. 5. ReferringFIG. 5, it is shown that round uniform nanoparticles of 15-20 nm sizewere generated.

Example 3

Nickel chloride 18 g, Na-CMC 12 g, ethanol 150 g, and toluene 150 g wereadded to 300 g of distilled water, and the aqueous mixture was stirredat 40° C. 30 g of hydrazine hydrate was added to the reversemicroemulsion and it was stirred for 30 minutes to form nickel-hydrazinecomplex. 0.03 mole of NaBH₄ was added to the reverse microemulsionincluding the nickel-hydrazine complex, and it was stirred for 1 hour toproduce nickel particles by reduction. Nickel nanoparticles wereseparated from the reverse microemulsion by centrifugation. Afterwashing the separated nanoparticles with acetone and distilled water 3times, nickel nanoparticles were obtained by drying in a vacuum dryingoven at 50° C. for 3 hours.

Further, a photo of SEM (Scanning Electron Microscope) of nickelnanoparticles produced by example 3 is illustrated in FIG. 6. ReferringFIG. 6, it is shown that round uniform nanoparticles of 30-40 nm sizewere generated.

Comparison Example 1

Nickel chloride 18 g, PVP 60 g, ethanol 150 g, and toluene 150 g wereadded to 300 g of distilled water, and the aqueous mixture was stirredat 40° C. 0.03 mole of NaBH₄ was added to the reverse microemulsionincluding the nickel-hydrazine complex, and it was stirred for 1 hour toproduce nickel particles by reduction. Nickel nanoparticles wereseparated from the reverse microemulsion by centrifugation. Afterwashing the separated nanoparticles with acetone and distilled water 3times, nickel nanoparticles were obtained by drying with vacuum dryingoven at 50° C. for 3 hours.

Though the nickel nanoparticles produced by comparison 1 was 15-20 nm,the shape was not uniform and agglomeration was so high thatnanoparticles having proper distribution were not formed.

In example 1, 4 g of nickel nanoparticles were obtained from 18 g ofnickel chloride. After the nickel nanoparticles were re-dispersed inethanol and centrifuged at 3000 rpm for 5 minutes, 3.5 g of nickelnanoparticles having dispersion stability were obtained by removingprecipitates. In examples 2 and 3, similar results were obtained, whichwere determined by same analyses.

On the contrary, in comparison example 1, when nanoparticles werere-dispersed as in example 1, it is noted that agglomeration was so highthat nickel nanoparticles having dispersion stability were not obtainedby centrifugation at 3000 rpm for 5 minutes.

Examples 4 to 10

Nickel nanoparticles were manufactured as in example 1, except thatnickel chloride and each kind of surfactants were added as shown inTable 1. This is to confirm the relation between size of nickelnanoparticles and content of nickel precursor and surfactant. The sizeof manufactured nickel nanoparticles was determined and summarized inTable 1.

TABLE 1 Nickel Mean particle Chloride Surfactant size (nm) Example 4 7 gPVP 14 g 34 Example 5 7 g PVP 35 g 18 Example 6 40 g  PVP 14 g 55Example 7 2 g Na-CMC 6 g 35 Example 8 7 g Na-CMC 6 g 52 Example 9 2 gCTAB 22 g 8 Example 10 7 g CTAB 22 g 17

As shown in Table 1, the lower the content of nickel precursor is andthe higher the content of surfactant is, the smaller size of nickelnanoparticles are produced.

Production of Conductive Ink

The nickel nanoparticles were added to diethylene glycol butyl etheracetate and an aqueous solution of ethanol, and dispersed with an ultrasonicator to produce 20 cps of conductive ink. The conductive ink thusproduced may be printed on a circuit board via inkjet techniques to formconductive wiring.

Multi Layer Ceramic Condenser

Nickel powders manufactured according to examples 1-3 were dispersed ona binder to produce nickel paste having high viscosity. After the pastwas coated by screen printing on a ceramic conductive layer of bariumtitanate and dried, multilayers were then stacked thereon, pressed, andcalcined at 1300° C. under reductive condition to produce MLCC.

Further, an internal electrode may be formed by calcining underreductive condition after the conductive ink set forth above is inkjetprinted on the ceramic conductive layer of barium titanate and dried.

Although a few embodiments of the present invention have been shown anddescribed, it will be appreciated by those skilled in the art thatchanges may be made in these embodiments without departing from theprinciples and spirit of the present invention, the scope of which isdefined in the appended claims and their equivalents.

1. Nickel nanoparticles comprising: an aqueous solution including anickel precursor, a surfactant, a hydrophobic solvent, and distilledwater, the hydrophobic solvent being one or more compounds selected fromthe group consisting of hexane, cyclohexane, heptane, octane, isooctane,decane, tetradecane, hexadecane, toluene, xylene, 1-octadecene, and1-hexadecene; a compound including hydrazine which is added to theaqueous solution to form a nickel-hydrazine complex; and a reducingagent added to the compound including the nickel-hydrazine complex. 2.The nickel nanoparticles of claim 1, wherein the nickel nanoparticleshave 10-50 nm of uniform size, smooth surface and superior dispersionstability.
 3. The nickel nanoparticles of claim 1, wherein the nickelnanoparticles include 90-97% of nickel content.
 4. Conductive inkincluding nickel nanoparticles of claim
 1. 5. A multilayer ceramiccondenser including nanoparticles of claim 1 as an electrode material.